Here in this quotation of the Lord’s prophecy to Lehi, there was originally an and in the original manuscript before the first inasmuch. Oliver Cowdery definitely wrote an ampersand there in 𝓞. But right in front of the &, he initially wrote some other letter, which he immediately erased. The erasure of this letter, no longer legible, led him to smear the ink onto the adjacent ampersand. The smearing looks like a couple of very thin ink strokes across the ampersand, but it definitely does not resemble Oliver’s normal crossout. Yet when Oliver copied this passage into 𝓟, these seeming strokes led him to think that the ampersand had been crossed out, so he ended up omitting the and in 𝓟. The critical text will restore the and here.
Since the standard text for this passage has no conjunctive connector before the first inasmuch, there has been considerable variation with respect to the punctuation for that inasmuch-clause:
Editors and typesetters for the printed editions have struggled to determine whether the first inasmuch-clause belongs to the preceding or following main clause. Since the original text actually read and inasmuch, the inasmuch-clause clearly belongs to the following main clause:
Every time the text repeats the Lord’s promise to Lehi and Nephi about keeping the commandments and prospering in the land, the subordinate inasmuch-clause referring to keeping the commandments comes first, as in the following parallel examples that give Lehi’s own language for this promise:
For a list of the many citations in the Book of Mormon of this promise (given originally to Lehi and to Nephi), see under 2 Nephi 1:20.
I also note here that the preceding parenthetical statement “and they shall be blessed” in Alma 50:20 can be found in Lehi’s discourse to the sons and daughters of Lemuel:
Thus it would be textually wrong in Alma 50:20 to connect the inasmuch-clause to the standalone statement “and they shall be blessed”.
Summary: Restore in Alma 50:20 the and that Oliver Cowdery wrote in 𝓞 as an ampersand right before the first inasmuch; the punctuation should be adjusted so that this inasmuch-clause belongs to the following main clause (“they shall prosper in the land”), not to the preceding parenthetical statement (“and they shall be blessed”).